The production of finished workpieces from blanks traditionally is accomplished by the use of a series of forming presses or stations arranged longitudinally in a row wherein a workpiece is fed to a forming die at one end of the row that changes the shape of the workpiece. Although a finished part can be made in one forming operation, it is more common to use three to ten successive forming operations to produce a finished part from a blank. Each forming operation normally uses a forming die that is made to reshape or reform the workpiece that is delivered to such die. Each die normally comprises a die set having vertically adjustable upper and lower halves that move relative to one another following delivery of a workpiece between the die halves so that relative movement of the halves toward one another engages and reforms the workpiece.
Apparatus for performing successive forming operations on a workpiece may comprise a single forming press having a plurality of forming dies within the press to each of which a workpiece is moved in succession. This type of forming press is known as a transfer press and, once the workpiece has been introduced to one end of the press, it is transferred from die to die by transfer means contained wholly within the press. A transfer press conventionally produces a finished part.
Another type of apparatus for forming workpieces comprises a progressive die press wherein all the dies are contained within a single press. In this case, however, a strip of material is fed into one end of the press and the part is made by stamping the strip at successive die forming stations leaving the part attached to the strip until the last die operation at which the part is cut free from the strip. The movement of the workpiece from die to die is carried out by movement of the strip to which the workpieces are attached, thereby requiring no workpiece transfer apparatus other than the strip feeder itself. However, because of the need to keep the workpieces attached to the strip until the final die operation, there can be excessive scrap. Further, the dies need to be maintained quite close together thereby complicating the construction and exchange of the dies.
There also exists what is known as a tandem press line which comprises a plurality of individual forming presses arranged in a row with each of the presses being uniformly spaced from one another. In a tandem press line a workpiece is delivered to the press at one end of the row and shaped by operation of that press. The workpiece then is transferred from the first press across the space between the first press and the next adjacent press, following which the workpiece is transferred to the adjacent press and again shaped. This procedure is repeated for each of the presses in the row.
In all of the systems referred to, it is necessary to provide for delivery of the workpiece into the first press or die station, transfer of the workpiece from the first press or die station to the next, and transfer of the finished workpiece from the final press or die station to some kind of workpiece receiver.
The handling of the workpiece during its transfer to and from the presses has resulted in severe problems. It is preferable to transfer the workpiece by some kind of automatic material handling apparatus because such apparatus is faster, frequently less expensive, and less dangerous to personnel and to the workpieces themselves as compared to manual transfer.
Automatic material handling systems for presses can take various forms. Typically, special purpose overhead lift, carry, and place mechanisms are used to load and unload the presses by means of vacuum cups or grippers. Such mechanisms also may be used to transfer workpieces between the presses.
When a change in the workpieces to be formed is made it is necessary to change the die sets in the presses. This usually necessitates the provision of equipment to relocate the workpiece transfer apparatus to enable the die sets in the presses to be replaced by other die sets. The conventional transfer apparatus is supported on a floor mounted framework at one end of the row of presses, as well as between adjacent presses, although in some installations it is possible to raise, lower, or bodily move the transfer apparatus to positions in which the die sets may be moved into and out of the presses.
There are many kinds of automatically operable material handling or workpiece transfer devices for use in press line applications. For example, there are lift and carry shuttles, conveyors, robotic arm devices, and articulated arm units which function to transfer a workpiece from one position to another in timed relation to the operation of the presses.
Regardless of the type of workpiece transfer devices that have been used, all must be removed from the press line to allow die exchanges to be performed or to permit access to the die for maintenance or other operations.
Forming presses make use of die sets composed of upper and lower halves for the manufacture of each part or, more precisely, for each operation needed to make the finished part. The presses in the press lines are capable of operating on more than one specific part thereby necessitating exchanging of a die set designed for forming one part with another die set for forming a different part, and vice versa. To enable the exchange to be made efficiently, the workpiece transfer apparatus must be relocated or adjusted to avoid interference between the transfer apparatus and the die sets and the apparatus by means of which the exchange is effected.
In modern press installations a single press can run hundreds of parts without any change of the dies, but it is more common to run between five to twenty parts per press for most production processes. Since the dies can be quite large and heavy, e.g., 1 to 75 tons, exchanging one set of dies for another heretofore has been a difficult process that can require as much as an entire production shift to perform. If a production run is limited to a small number of parts, a large number of die changes are necessary. If six to eight hours are required for each exchange, production time is limited severely.
Die changing equipment has been developed and is in use which enables the exchanging of dies to be performed relatively quickly. Part of this equipment comprises a movable die cart having wheels which ride on floor tracks between positions in which a die set can be moved from the cart into a press from one side thereof while the die set previously in the press simultaneously is moved out of the press onto another cart that is positioned on the opposite side of the press.
Die carts enable the elimination of a great deal of time required to effect press changeover. In a tandem press line, for example, the carts move into position at each end of the press line as well as between adjacent presses and effect exchange of the dies. Many different die exchange arrangements can be used effectively, with anywhere from one to four or more presses being serviced by each die cart. The die carts, when not in use in exchanging dies, normally are parked in an area remote from the presses so as to provide room for personnel and the workpiece transfer apparatus during operation of the press. For example, a so-called "domino" process can change the dies in a tandem press line, or a transfer/progressive/blanking press in three simple steps. This process uses one more die cart than the number of presses and the three steps are: (1) preload all of the die carts except one with a "new" die set and move the carts into the press line, the empty die cart being located at one end of the press line; (2) drive the "old" die sets from the associated presses in a direction toward the empty die cart simultaneously, thereby enabling the "old" die sets to move from the presses onto the die carts as the "new" die set is being inserted into the adjacent press; and (3) move the die carts now carrying the "old" die sets out of the line of presses. In this operation the die cart initially having no die set will bear one of the "old" die sets, whereas the die cart at the opposite end of the line will not carry a die set.
Die carts which function in the described manner have been manufactured heretofore by Atlas Technologies, Inc., of Fenton, Mich., and are in use worldwide.
Following removal of the die carts and the "old" die sets from the line of presses, material handling apparatus for transferring the workpieces into and out of the presses is positioned in the spaces between adjacent presses, and the die carts are parked in an area remote from the presses.
Although the use of a movable die cart to facilitate die exchanges has many benefits, available floor space in many existing facilities imposes severe limitations on the use of movable die carts. In many large press facilities, the physical plant was designed and constructed many years ago, and such designs were dictated by economics and then available materials. In many instances a series of parallel tandem press lines was used including two press lines per bay and having an overhead crane for moving die sets. In some cases the crane tracks spanned the width of the bay so as to be perpendicular to the press rows, whereas in other instances the crane tracks and press rows paralleled one another. Conventionally, the two parallel press lines have adequate spacing between them to form an aisle for movement of the die sets to and from the presses as well as accommodating the need for access space for press maintenance. Conventionally a smaller aisle on each of the outer edges of the building's bay is provided, but such aisles usually are quite narrow because of the foundation requirements for the presses, crane track supporting. columns, and the like.
In most cases the older press facilities provide no allowance for either die carts or movable material handling apparatus because they relied upon manual handling of the parts between the presses and therefore had no need to provide floor space for automatic material handling apparatus at the ends of the rows and between adjacent presses. Neither was any allowance made for parking any type of movable die or other cart remote from the presses when the presses were in operation. Consequently, the benefits available from the use of movable die carts for rapid die exchange were difficult to achieve in some of the older facilities.
One partial solution to the problem involved the use of what is known as "sister" press lines wherein two nearly identical, parallel rows of presses could be serviced by one line of carts located in the central aisle between them. This solution necessitated that the two rows of presses be nearly identical and also restricted the scheduling flexibility since the die sets in the two rows could not be exchanged at the same time. Further, die prestaging for each line could require several hours' delay from one row to another while waiting on cranes to unload "old" dies from one row of presses to make room for prestaging the "new" dies for the other row. In addition, the die carts had to park in the center aisles because the outer aisle, i.e., those next to the walls of the building, were not accessible by the cranes because the crane tracks were not long enough.
As a result of the inability of the older facilities to accommodate the die cart die exchange system, it has been necessary to park the die cart in positions between parallel rows of presses and to move and park any workpiece transfer apparatus associated with the presses in the aisles alongside the building walls, thereby losing the use of the aisles for traffic and maintenance access. In addition, the space between adjacent rows of presses conventionally is incapable of accommodating more than one die cart, thereby necessitating utilization of the "sister" concept or limiting the ability of the die carts to serve as only one of the two lines.
A principal object of the invention is to overcome the problems referred to above.